Recent research has revealed that foreshore beach sands, can act as reservoirs for toxic concentrations of the cyanotoxin microcystin, commonly produced during harmful algal bloom (HAB) events. Foreshore sands, situated on coastal shorelines, are constantly rewetted by waves and therefore subject to a continuous input of algae during bloom events. This phenomenon poses significant human health and beach management challenges, especially for children who are more likely to come into contact with contaminated water and sand. Our study focused on three Ohio beaches: Maumee Bay State Park Beach in Oregon, Lakeview Beach in Lorain, and Huntington Beach in Bay Village. Using indirect, competitive ELISA to measure microcystin concentrations, we found that about 8% water samples had levels above the EPA no-contact threshold for recreational waters. The highest microcystin concentrations were most frequently observed at Maumee Bay State Park Beach in Oregon.
To investigate the persistence of microcystin in foreshore sands, we conducted laboratory studies using autoclaved and non-autoclaved sand microcosms spiked with Microcystin. The sandy microcosms were incubated at 10% moisture and 30°C or 0% moisture and 10 °C for 49 days, and samples were periodically analyzed using Enzyme-Linked-Immunosorbent-Assay (ELISA). Results indicated that microcystin concentrations decreased by 46% in autoclaved treatments and by 100% in non-autoclaved treatments, with rapid, total degradation occurring between 21 and 28 days in non-autoclaved sands. This persistence suggests that microcystin can remain in the foreshore sands long after visible algae have disappeared, posing a lingering risk for beachgoers.
To understand the potential for human exposure to microcystin through skin contact during recreational beach activity, we employed vertical static diffusion cells (Franz Cells) with pig skin as a surrogate for human skin. We tested microcystin permeation under various conditions: unaltered skin, skin with abrasions, and skin treated with sunscreen, suntan accelerators, and aloe vera, which are representative of skin conditions of beachgoers. Our findings showed that skin condition and treatments significantly influence microcystin absorption rates, highlighting the potential health risks associated with recreational beach exposure during HAB events.
These findings highlight the importance of considering foreshore sands as a potential vector for cyanotoxin exposure in humans, necessitating better beach management practices, public health advisories to protect vulnerable populations, and the need for coastal resilience. Further research into the persistence, occurrence, and exposure pathways in humans of microcystin is crucial for developing comprehensive strategies to mitigate the risks associated with HABs in coastal and beach environments.
